It is standard to regrind sprues, runners, excess parison material, and reject parts, to plastify this reground material, and to mix it at a certain ratio with virgin compound for remolding. This system is described in detail in East German patent 231,029 of F. Endler, in German patent documents 2,815,271 of H. Geng, 2,845,650 of R. Schmidt (European equivalent application 10,688), and 3,538,116.
It is also known from German patent document 1,729,323 of E. Friederich to combine two or more streams of virgin synthetic-resin material to make a laminated article.
The recycling of synthetic resins is, however, fraught with difficulties mainly because the used containers and the like normally carry paint, metals, and various other impurities including noncombustible organic materials. Thus as described in "Verschiedenartige `Abfalle` im Griff" (Plastverarbeiter, 1984, No. 4) and "Wiederverserten von thermoplastischen Kunststoffabfalle in der Extrusion (I)" (Kunststoffberater, 1989, No. 3) it is known to sort the plastic scrap, grind it up, plastify the particles into a stream, filter the stream, and extrude the stream as particles that are cooled into a bulk granulate. The resultant product is particles of recycled plastic that can be replastified and reused. This procedure is fairly complex so that there is no significant saving in the use of recycled material over the use of virgin material.